1. Field of the Invention
The present invention relates to a band brake apparatus of a rotating machine and particularly to a dual band brake apparatus for stopping, or at least retarding, the motion of a rotating machine, such as a washing machine having a large capacity.
2. Description of the Prior Art
A conventional brake apparatus being used in the industrial field is provided with a single lever 30 and single band 20, as shown in the accompanying FIGS. 3 and 4. The flexible steel band 20 acts against the external surface of a cylindrical drum 10 through rotation of the operating lever 30 in a clockwise direction about a pivot 40.
If the drum 10 is rotating in a clockwise direction, the force applied to the lever 30 is less than would be the case if the drum 10 were instead rotating in the counterclockwise direction. With this lesser force, the braking application for stopping, or at least retarding, the clockwise motion of the drum is accomplished. Since an inertial force of rotation of the drum is converted into a friction force, the friction force is added to a braking force.
If the drum 10 is rotating in a counterclockwise direction, the direction of the friction force mentioned above is reversed. The braking application performed in this case requires more force than in the case of the clockwise drum rotation.
It is generally desirable that the braking action applied to a rotary drum be consistent. In the case where the drum is capable of rotation in only one direction, a consistent braking action can be achieved by a conventional braking mechanism depicted in FIGS. 3 and 4. However, for reasons explained above, consistent braking action cannot be achieved by such a braking mechanism in the case where the drum is reversible, i.e., when the drum is able to rotate in either direction.
In order to achieve a consistent braking force, regardless of the direction in which a reversible drum rotates, braking mechanisms of the types disclosed in Japanese Laid-Open Publication Nos. SHO 60-237230 and SHO 56-14630 have been proposed.
The band brake apparatus disclosed in Japanese Laid-Open Publication No. SHO 60-237230 includes a single flexible band lined with a friction material. The band encircles an external surface of a cylindrical drum, one band end being connected to one connecting shaft at the end of a drive lever, the other band end being connected to another connecting shaft at the end of the drive lever. The connecting shafts are interconnected by gears so that both shafts are rotated in response to rotation of the drive lever in such manner that both ends of the brake bands are pulled toward one another. The connecting shafts are normally pulled toward each other by a spring which yields in response to rotation of the drive lever in a brake-actuating direction.
The band brake apparatus disclosed in Japanese Laid-Open Publication No. SHO 56-14630 includes a single flexible band one end of which is attached to a first lever and another end of which is attached to a second lever. The band encircles the external surface of a cylindrical drum. A torsion spring engages the first and second levers to bias them outwardly. First and second stops are provided for restraining rotation of the second lever around a fixed shaft of the torsion spring within a predetermined range. A third stop is provided for restraining the rotation of the first lever around the small shaft of the operating lever, whereby the torsion of the torsion spring causes both ends of the band to move upwards against the rotating drum so as to brake the rotating drum.
The prior art apparatuses which require elements such as springs and gears, exhibit weaknesses in durability, higher manufacturing costs and complicated structure.
Furthermore, the prior art apparatuses have the problem of a shorter life cycle caused by damage of the elements.
An object of the present invention is to provide a band brake apparatus for solving the above problems.